Electrical rheostat.



Patented Sept. ll, I900.

H. W. LEONARD.

ELECTRICAL RHEOSTAT.

(Application filed Feb. 11, 1899.)

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UNITED STATES.

P TENT OFFICE.

HARRY WARD LEONARD, OF NEW YORK, N. Y.

ELECTRICAL RH EOSTAT.

PECIFICATION forming part of Letters Patent No. 657,703, dated September 1 1, 1900.

Application filed February 11, 1899. gerial No. 705,288. (No modeLl To all whom, it may concern.-

Be it known that I, HARRY WARD LEON- ARD, a citizen of the United States, and a resident of the borough of Manhattan, in the city of New York, county and State of New York, have invented a certain new and useful Improvement in Electrical Rheostats, of which the following is a specification.

My invention relates to rheostats, and especially to that type of rheostat in which there is developed a large amount of energy for a comparatively-short period and then there occurs a considerable interval of rest, as is the case with most rheostats employed for starting and accelerating to full speed electric motors which ordinarily run at full speed.

In carrying my invention into effect the resistance material is suspended from or otherwise mounted upon a slab of insulating materialsuch as slate, marble, porcelain, pottery, glass, terra-cotta, or any other natural or artificial equivalent and suitable material. The slab should preferably be of fireproof material; but that is not essential in all cases. The resistance so suspended or mounted is placed within a shallow box of which the slab constitutes the top or cover. Upon the front or exposed surface of the slab I mount the contact plates or buttons, contact-levers, binding-posts, magnets, due. The interior of the box is quite shallow, the space between the resistance and the Walls of the box, when made of metal or other conducting-material, being only such as required for insulating purposes. After the resistance is placed in position I preferably lill up the entire air-space with an insulating material, such as sand or other mineral insulating material in granular or powdered form. The granulatedinsulating material maybe mixed with Water and the box filled therewith after the resistance is in position and. the whole subsequently subjected to heat to dry the insulating material. Instead of a material like sand an adhesive material, such as Portland cement, may be employed for insulating the resistance and filling the box. I prefer, however, to employ sand on account of its cheapness, its insulating properties, its heat-conductive properties, its specific capacity for heat, and its inertness where exposed to heat the bottom.

and chemical action, and, flllhl16l,.f0l the reason that the resistance is free to expand and contract therein withoutinjury; further, for the reason that the box can be readily filled therewith after the resistance is placed in position; further, for the reason that the resistance can be readily embedded in the sand if the box is first filled therewith, and, further, for the reason that the resistance material can be readily removed for inspection or repairs. The resistance material is preferably of metal in the form of wire in rheostats for small currents and in the form of a ribbon in rheostats for large currents. Any known form or kind of resistance material, however, might be employed. When metal in Wire or ribbon form is employed, it is preferably coiled or reflexed and arranged in loops between the inner ends of the contact plates or buttons, thus forming steps or sections. The shallow box, except the cover, is preferably made of metal; but it may be made wholly or partially of non- :metallic materials-such as porcelain, pottery, terra-cotta, slate, glass, &c. When the box is made partially of metal, I prefer to make the sides of metal, cast in one piece and constructed to support a slab of any of the insulating materials above named to form In some forms the top or cover of the box may be made in two parts, one part being of slate or any of the equivalent materials above named and which will carry the contact plates or buttons and have the resistance attached thereto, While the other part may be of metal. In another form a part of the top may be cast integral with the side walls and bottom of the box, or it may be otherwise rigidly secured thereto, and the other part of the top will be of slate or other equivalent material and carry the contactbuttons, resistance, &c. In some forms where metal is employed in the construction of the box the inner surface may be coated or lined with a suitable insulating material. In practice I prefer to make the shallow box of castiron, cast in one piece without a cover and having supporting-feet or studs, and a cover of slate or equivalent material in one piece and carrying the resistance, contact plates or buttons, contact-lever,binding-posts for circuit connections, and other parts employed in.

connection therewith. Such cover is secured to the box by screws or otherwise, and a suitable sealing material is placed between it and the upper edges of the box to form a suffieiently-tight joint. I have also found it desirable to provide a layer of non-heat-conducting material, such as asbestos, between the resistance and the cover to prevent the cover becoming hot and cracking.

My invention is illustrated in the accompanying drawings, in which Figure 1 is a top plan view or front elevation; Fig. 2, a vertical cross-section on the line 2 2 of Fig. 1; Fig. 3, a plan view of the box with the top plate and resistance removed; Fig. 4, a view of the inner side of the top plate, showing the resistance attached thereto; Fig. 5, a View similar to Fig. 1, illustrating the modified form of box having a top plate or cover made in two parts, one part being made of insulating material designed to carry the resistance, contactbuttons, and binding-posts and the other part made of metal and upon which the contactlever and other devices will be mounted and suitably insulated; Fig. 6, a vertical crosssection on the line 6 6 of Fig. 5; Fig. 7, a vertical cross-section of a box having a separable bottom plate; Fig. 8, a vertical crosssection of a box, in which a part of the top plate is formed integral with the side walls and having a removable part, of insulating material, designed to carry the resistance, binding-posts, and contact-buttons, and a removable side wall; and Fig. 9, a plan view of the box of Fig. 8 with the removable portions removed.

Referring to Figs. 1 to 4, A is a shallow box which is preferably made of cast-iron in one piece and having supporting-feet a. This box, however, may be made of any other suitable metal or insulating material. hen the box is made of metal, I sometimes provide a thin lining a, of any suitable insulating material-such, for instance, as enamel or asbestos. The cover B is preferably of slate and in one piece and is secured in position by screws b. The joint between the box and cover is sealed with any suitable materialsuch, for instance, as puttya groove a being provided in the edges of the side walls to retain the sealing material. Upon the cover B is mounted a set of contact plates or but tons c, which project through the cover and have secured thereto at their inner ends clamping-plates c, which receive the resistance D. A contact-lever G, pivoted upon the cover, makes contact with buttons 0 to cut in or out the sections of the resistance. The resistance D may, as above stated, be of any suitable form or material, and when made of metal it may be either in the form of wire or ribbons, the latter form being shown in the drawings, and, as shown in Fig. 4, the ribbon is refiexed and arrangedin loops between the clamps c. In some instances, and particularly where the loops of the resistance are arranged close together, I employ pins (Z, either of metal or insulation, for holding each loop in position; but the sections of the resistanee between the clamps and pins are not attached to the plate B, and hence the resistance is entirely free to expand or contract, due to changes in temperature, without straining or otherwise weakening or injuring the resistance or its attachment to the cover B. The air-space in the box is filled with any suitable insulating material, preferably in granular or powdered form, and in practice I prefer to employ sand for the rea sons above stated; When the cover is not made of fireproof material or of a material which is liable to crack when subjected to high heat, as is the ease with slate, Iprovide a layer F of non-heat-condueting material, such as asbestos.

In the form of apparatus shown in Figs. 1 to 3, the box may be first filled with sand, and afterapplyingthesealingmaterial to the edges of the side walls or cover of the box the cover, with the resistance attached, is placed in position, the resistance readily embedding itself in the sand. The cover, with the resistance, may, however, be placed in position be fore the box is filled with sand, the sand in that case being poured into the box through the hole in the upperside wall. (See Fig. 2.) This hole is screw-threaded and is closed by a screw-plug a When the box is filled in this way, the sand is first heated, so that it will be perfectly dry and run freely. It will be observed that in the form of rheostat just described the slate-cover, with the resistance and cooperating parts, constitutes in itself a complete and operative rheostat and that the addition of the box and filling material serve mainlyasheat-absorbing elements. In Figs. 5 and 6 the same construction is shown, except that the cover is made in two parts. One part B is made of slate or other equivalent material and carries the contact-buttons c and the resistance D, and the other part 15 is made of metal. The contact-lever C is pivoted upon part B and suit-ably insulated. To seal the joiutbetween the two parts of the cover, part B is provided with an overlapping fiange I), having a groove to receive the sealing material. Flange b also aids in holding part B in position. In this form the sand-filling maybe put in either before or after cover B and resistance D are placed in position, and in either case it will be possible to see that the sections of the resistance are properly separated before entirely closing the box. Cover B may be provided with a layer a of insulating material to prevent the resistance from making electrical contact therewith.

In Fig. 7is shown a box which may have a cover made in one piece, as in Fig. 2, or in two parts, as in Fig. 6; but instead of having a bottom formed integral with the side walls I provide a flange c for supporting a bottom plate E, of metal or insulating material. In

practice this bottom plate will be secured in position by screws or otherwise, but preferably so as to be removable, and the joint is sealed in the same manner as the cover, the groove for sealing material being shown at e.

In Figs. 8 and 9 I have shown a form of box in which a part of the cover A is formed integral with the bottom and side walls. The resistance, contact -buttons, and bindingposts are carried by the cover B, which is made of slate or equivalent material and is held in position by screws or otherwise. The joints are sealed, as in the other forms described, the grooves a being in the side walls and top portion A, as shown in Fig. 8. In this form the cover B, with the resistance, is placed in position before the box is filled with sand. The sand is put in at the upper side opening, which is closed by a plate A held by screws or otherwise and sealed. The grooves (L2 for the sealing material at these joints are formed in the plate A What I claim is- 1. A motor-starting or equivalent rheostat composed of a shallow box, one side of which is made wholly or partially of insulating material and carries the resistance and contactplates, the resistance being inside of the box arranged in steps connected with the contact-plates and lying in a plane parallel to the top and bottom of the box, and embedded in a mineral insulating material, which insulates the sections of the resistance from each other and prevents overheating of the resistance by absorbingthe heat developed therein.

2. A motor-starting or equivalent rheostat composed of a shallow metal box, one side of which is made wholly or partially of insulating material and carries the resistance and contact-plates, the resistance being inside of the box arranged in steps connected with the contact-plates and lying in a plane parallel to the top and bottom of the box and embedded in a mineral insulating material which insulates the sections of the resistance from each other and prevents overheating of the resistance by absorbing the heat developed therein.

3. A motor-starting or equivalent rheostat composed of a shallow cast-iron box, one side of which is made wholly or partially of insulating material and carries the resistance and contact-plates, the resistance being inside of the box arranged in steps connected with the contact-plates and lying in a plane parallel to the top and bottom of the box and embedded in a mineral insulating material which insulates the sections of the resistance from each other and prevents overheating of the resistance by absorbing the heat developed therein.

4. A motor-starting or equivalent rheostat composed of a shallow box, one side of which is made wholly or partially of insulating material and carries the resistance and contactplates, the resistance being in the form of aconnected with the contact-plates and lying in a plane parallel to the top and bottom of the box, and embedded in a mineral insulating material.

5. A motor-starting or equivalent rheostat composed of a shallow cast-iron box, one side of which is made wholly or partially of insu lating material and carries the resistance and contact-plates, the resistance being in the form of a ribbon inside of the box arranged in steps connected with the contact-plates and lying in a plane parallel to the top and bottom of the box, and embedded in a mineral insulating material.

6. A motor-starting or equivalent rheostat composed of a shallow box, one side of which is made wholly or partially of insulating material and carries the resistance and contactplates, the resistance being inside of the box arranged in steps connected with the contactplates and lying in a plane parallel to the top and bottom of the box and embedded in a granular or powdered insulating filling material which insulates the sections of the resistance from each other and prevents overheating of the resistance by absorbing the heat developed therein.

7. A motor-starting or equivalent rheostat composed of a shallow cast-iron box, one side of which is made wholly or partially of insulating material and carries the resistance and contact-plates, the resistance being inside of the box arranged in steps connected with the contact-plates and lying in a plane parallel to the top and bottom of the box and embedded in a granular or powdered insulating fill-- ing material which insulates the sections of the resistance from each other and prevents overheating of the resistance by absorbing the heat developed therein.

8. A motor-starting or equivalent rheostat composed of a shallow cast-iron box, one side of which is made wholly or partially of insn lating material and carries the resistance and contact-plates,the resistance beingi n the form of a ribbon, inside the box arranged in steps connected with the contact-plates and lying in a plane parallel to the top and bottom of the box, and embedded in a granular or powdered insulating filling material which insu lates the sections of the resistance from each other and prevents overheating of the resistance by absorbing the heat developed therein.

9. A motor-starting or equivalent rheostat composed of a shallow box, having a top or cover made of slate or equivalent material, and which carries the resistance, contactplates and contact-lever, the resistance being inside the box arranged in steps connected with the contact-plates and lying in a plane parallel to the top and bottom of the box, and embedded in a filling of sand.

10. A motor-starting or equivalent rheostatcomposed of a shallow box, having a top or cover made of slate or equivalent material, and which carries the resistance, contactplates and contact-lever, the resistance being inside the box arranged in steps connected with the contact-plates and lying in a plane parallel to the top and bottom of the box, and embedded in a filling of sand, and a layer of non-heat-conducting material between the resistance and the cover.

11. A motor-starting or equivalent rheostat composed of a shallow box, having a top or cover made of slate or equivalent material, and which carries the resistance, contactplates and contact-lever, the resistance being in the form of a ribbon inside the box arranged in steps connected with the contactplates and lying in a plane parallel to the top and bottom of the box, and embedded in a filling of sand.

12. A motor starting or equivalent rheostat composed of a shallow cast-iron box, having a top or cover made of slate, or equivalent material, and which carries the resistance, contact-plates and contact-lever, the resistance being in the form of a ribbon inside the box arranged in steps connected with the contactplates and lyingin a plane parallel to the top and bottom of the box, and embedded in a filling of sand.

13. A motor-startin g or equivalent rheostat composed of a shallow east-iron box, having a top or cover made of slate, or equivalent material, and which carries the resistance contact-plates and contact-lever, the resistance being in the form of a ribbon inside the box arranged in steps connected with the contactplates and lying in a frame parallel to the top and bottom of the box, and embedded in a filling of sand, and a layer of non-heat-conducting material between the resistance and the cover.

14:. A motor-starting or equivalent rheostat composed of a shallow box having a top or cover, made of slate or equivalent material, the resistance being held to the inner side of said cover by clamps attached to the shanks of contact-plates which project through the cover, and said cover also having pins on its inner side around which the resistance is looped, and a filling of sand in said box, in which the resistance is embedded.

15. A motor-starting or equivalent rheostat composed of a shallow cast-iron box having a top or cover, made of slate or equivalent material, the resistance being held to the inner side of said cover by clamps attached to the shanks of contact-plates which project through the cover, and said cover also having pins on its inner side around which the resistance is looped, and a filling of sand in said box, in which the resistance is embedded.

16. A motor-starting or equivalentrheostat composed of a shallow box having a top or cover, made of slate or equivalent material, the resistance in the form of a ribbon being held to the inner side of said cover by clamps attached to the shanks of con tact-plates which project through the cover, and said cover also having pins on its inner side around which the resistance is looped, and a filling of sand in said box, in which the resistance is embedded.

17. A motor-starting or equivalent rheostat composed of a shallow cast-iron box having a top or cover, made of slate or equivalent material, the resistance in the form of a ribbon being held to the inner side of said cover by clamps attached to the shanks of contactplates which project through the cover, and said cover also having pins on its inner side around which the resistance is looped, and a filling of sand in said box in which the resistance is embedded.

18. A motor-starting or equivalent rheostat composed of a shallow cast-iron box having a top or cover, made of slate or equivalent material, the resistance in the form of a ribbon being held to the inner side of said cover by clamps attached to the shanks of contactplates which project through the cover, said cover also having pins on its inner side around which the resistance is looped, a filling of sand in said box in which the resistance is embedded, and a layer of non-heatconduct-ing material between the resistance and the cover.

This specification signed and witnessed this 9th day of February, 1899.

H. XVARD LEONARD.

Witnesses:

AacHIBALn G. Rnnsn, JNo. R. TAYLOR. 

